The present invention relates to stabilizing fuel by deoxygenation, and more particularly to a heat exchanger fuel stabilization unit.
Fuel is often utilized in aircraft as a coolant for various aircraft systems. The presence of dissolved oxygen in hydrocarbon jet fuels may be objectionable because the oxygen supports oxidation reactions that yield undesirable by-products. Dissolution of air in jet fuel results in an approximately 70 ppm oxygen concentration. When aerated fuel is heated between 350 degrees F. (or 177 degrees C.) and 850 degrees F. (or 454 degrees C.), the oxygen initiates free radical reactions of the fuel resulting in deposits commonly referred to as “coke” or “coking”. Coke may be detrimental to the fuel lines and may inhibit combustion. The formation of such deposits may impair the normal functioning of a fuel system, either with respect to an intended heat exchange function or the efficient injection of fuel.
Various conventional fuel deoxygenation techniques are currently utilized to deoxygenate fuel. Typically, lowering the oxygen concentration to 2 ppm is sufficient to minimize coking problems.
One conventional Fuel Stabilization Unit (FSU) utilized in aircraft removes oxygen from jet fuel by producing an oxygen pressure gradient across a membrane permeable to oxygen. The FSU includes a plurality of fuel plates sandwiched between permeable membranes and porous substrate plates disposed within a housing. Each fuel plate defines a portion of the fuel passage and the porous plate backed permeable membranes define the remaining portions of the fuel passages. The permeable membrane includes Teflon or other type of amorphous glassy polymer coating in contact with fuel within the fuel passages for preventing the bulk of liquid fuel from migrating through the permeable membrane and the porous plate.
The use of a plurality of similarly configured flat plates increases manufacturing efficiency and reduces overall cost. Further, the size and weight of the FSU is substantially reduced while increasing the capacity for removing dissolved oxygen from fuel. Moreover, the planar design is easily scalable compared to previous tubular designs.